The article “Towards quantitative PET/MRI: a review of MR-based attenuation correction techniques” by Matthias Hofmann et al., European Journal of Nuclear Medicine and Molecular Imaging, 36 Suppl 1: pages S93 to S104 (2009) discloses a combined positron emission tomography (PET) and magnetic resonance (MR) imaging system, which produces an attenuation correction map based on an MR image acquired by an MR data acquisition unit. The attenuation correction map is used for reconstructing an attenuation-corrected PET image.
Since the physical origin of an MR image is not related to the attenuation of radiation generated during a PET scan, the quality of the attenuation correction map is reduced in comparison to, for example, an attenuation correction map that is produced based on a computed tomography (CT) image. However, MR images can contrast different tissue types such as water and fat which can be used to improve attenuation correction. Although CT images are known for spatial accuracy from which attenuation correction can be performed, CT images are not known for differentiating different tissue types which can impact attenuation correction. Furthermore, CT images use ionizing radiation to create the images while MR images are created using magnetic resonance.